Natural regeneration of alpine tundra vegetation after human trampling: A 42-year data set from Rocky Mountain National Park, Colorado, USA

摘要

The vegetation composition of four contiguous permanent plots was analyzed during 37 of 42 years between 1959 and 2001 to evaluate successional processes following the cessation of human trampling in alpine tundra. The plots were established adjacent to the Rock Cut parking lot at similar to 3658 m elevation along Trail Ridge Road in Rocky Mountain National Park, Colorado. Due to limitations in the original study design, the lack of true replication required that the plots be treated individually when subject to indirect ordination analysis to follow trends in overall plant composition and cover. The three most abundant species in the study plots were Artemisia scopulorum, Acomastylis rossii, and Kobresia myosuroides. At the beginning of the study in 1959, total cover ranged from 20 to 55% in the four plots. By 1961, three of the four plots achieved total canopy cover values of at least 100%. Vascular plant species richness (number of taxa per plot) averaged 20 in 1959, but by 1967 had nearly doubled to 37. During the first several years, rates of seedling emergence were high among most taxa with the notable exceptions of K myosuroides and A. rossii. However, likely due to desiccation and needle ice, seedling mortality was high. K myosuroides spread exclusively from remnant tufts, as did three species of cushion plants which survived the trampling. The overall decline in plant cover during the last two decades of this study, particularly for K myosuroides, indicates that long-term unassisted regeneration of severely degraded alpine tundra sites will take more than a century. While there have been periods of plant colonization and spread, climate factors such as a series of heavy snow years, and unchecked soil erosion from trails, can limit plant establishment and stop the recovery process, or push the recovery back by several decades. The negative influence of soil erosion, and quite possibly additional trampling, over a significant portion of the study plot points to the critical importance of using extreme care when establishing long-term monitoring plots, particularly in high-use areas.